*3.2.3. Monitoring of subclinical infections*

Some of the diseases in poultry have subclinical infections, like coccidiosis. The birds apparently seem health, but subclinical infections persist in birds over long periods of time, which have previously been infected with coccidiosis infections. On the day of vaccination, the birds should be closely monitored. The apparent health of flock should be analyzed. Moreover, the color and consistency of fecal droppings, abnormal sounds from birds, respiratory distress, etc. should be evaluated. After being satisfied with the proper health status of the bids, the concerned staff may be allowed to vaccinate the flock.

are properly washed and the vaccine is given to birds. The number of drinkers is increased in order to ensure that all the birds drink vaccine water. The water should be provided to birds in such a way that birds drink all the vaccine water within 2 h. The birds are regularly moved during this process so that all the birds drink water containing the vaccine virus. The stabilizers and coloring agents can be added in the vaccine. A tinge of the coloring agent can also be

Preventing Vaccine Failure in Poultry Flocks http://dx.doi.org/10.5772/intechopen.79330 89

Certain genes are discovered which have genetic resistance against viral diseases of poultry [44]. The breeding for disease resistance may provide good long-term solutions for disease control [45]. However, the emergence of new genetic groups and mutations require new vac-

Vitamin and mineral supplements help to develop immune response by acting on the immune cell or by changing metabolic or endocrine functions [47]; as a result, the antibodies are produced in the body at a faster rate and a protective level of antibodies is gained in a shorter time. Vitamin E and selenium have a role in modulating the immune response and have shown good results in preventing vaccine failure. Research conducted shows that vitamin E may enhance immune response to antigens in cockerels but excessive vitamin E may depress specific immune responses [48]. Administration of excess vitamins, amino acids, minerals and their combinations enhance the disease resistance by stimulating humoral and cellular immunity and phagocytosis [49]. Optimal vitamin nutrition is required for optimal immune response and disease resistance. The addition of higher levels of vitamin A, C, E and Selenium ensures better immune response of birds to vaccination and reduces the chances of vaccination failure in broiler poultry flocks [50]. Studies have suggested that the nutrient levels that are adequate for growth and feed efficiency may not be adequate for normal immunity for

The regular and continuous surveillance of prevalent diseases should be conducted in order to collect data on the disease pattern. For this purpose, the blood/serum and fecal samples may be collected and sent to the laboratory for diagnosis of disease. Moreover, the tracheal and cloacal swabs can also be sent to the laboratory for isolation of pathogens. The antibodies titer against injected vaccines may be got routinely checked for maintaining optimum titer of

Considerations regarding the use of live and killed vaccines should also be kept in mind during vaccination. The live vaccines may cause vaccine reactions and injection of killed vaccines may cause local tissue reactions. Therefore, only an expert professional or qualified veterinary assistant should be allowed to vaccinate the poultry birds. In general, vaccination should be

noticed on the beak of birds which indicates the drinking of water.

cine practices for successful immunization [46].

*3.2.10. Vitamin and mineral supplementation*

maximizing the resistance to disease [51, 52].

*3.2.11. Continuous surveillance*

antibody against the disease.

*3.2.12. General precautions*

*3.2.9. Host resistance*
